The invention relates generally to cold spray deposition processes, and, in particular, to methods of cold spraying feedstock including coated powder structures.
Bonded surface layers are desired for many applications including those in which the surfaces experience corrosion, erosion, or high temperature. One method used for producing bonded metallic coatings on substrates is cold spray technology. In cold spray technology (also referred to herein as simply “cold spray”), particles are mixed with a gas and the gas and particles are subsequently accelerated into a supersonic jet, while the gas and particles are maintained at a sufficiently low temperature to prevent melting of the particles. Copper coatings have been deposited using cold spray in which sufficient bonding among particles was achieved to produce bulk-like properties. However, higher temperature materials, such as stainless steel, nickel, nickel-base superalloys, and titanium-base alloys, are likely to require higher velocities to produce high quality deposits, challenging the limitations of conventional cold spray devices.
To attain better inter-particle bonding, and hence better deposit properties, using higher melting point metals than copper, a trend in cold spray technology is moving towards the use of higher gas temperatures. However, even high-temperature nitrogen gas is difficult to accelerate to the velocities required to achieve dense deposits of high-melting point materials such as nickel, iron, or titanium alloys. Therefore, helium gas is favored for these applications due to its substantially higher sound speed, relative to nitrogen. However, using helium gas for cold spraying is commercially challenging and in many cases, cost-prohibitive.
Therefore, there is a need for an economical method of making a high-quality bonded deposit of high-melting temperature alloys.